(a) Field of the Invention
The present invention relates to a process for the removal of nitrogen oxides (hereinafter referred to as NO.sub.x) from the waste gas containing said nitrogen oxides in conjunction with sulfur oxides (hereinafter referred to as SO.sub.x) and coming out of boilers, heating furnaces and incinerators by means of catalytic reduction resorting to ammonia as the reducing agent, which is characterized by using a catalyst composed of an active component containing iron or copper as the active metal and a specific carrier.
(B) Description of the Prior Art
In recent years, effective removal of NO.sub.x contained in the waste gases from various combustion systems has become an important task in view of the mounting public issue of air pollution prevention. The true status of affairs, however, is that technical developments for such removal are lagging behind those for the removal of SO.sub.x and a feasible commercial process has not yet been described.
For the so-called denitrification, i.e. removal of NO.sub.x from waste smokes, various processes have been proposed. Of these processes, the most promising from the practical point of view is the process which effects selective catalytic reduction by use of ammonia as the reducing agent. It is known that this method uses metals of platinum family and their oxides as the catalyst. In the reaction system in which SO.sub.x is present, however, such catalysts rapidly lose their catalytic activity and will not withstand prolonged use because of the poisonous effect of SO.sub.x. This is the principal reason that retards the method from practical use in spite of its outstanding features.